This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The study involves determination of a rate of in vivo actin polymerization in steady-state conditions, based on FRAP measurements. This collaborative study collaborative studies involves development of cell-biological models that have potential for generalization and implementation in the Virtual Cell. Such studies, where models are necessary for data analysis and/or better qualitative understanding of cell phenomena, serve as motivators (and at the same time as testbeds) for further development of the Virtual Cell.